Conventional systems for transmission of data over low impedance power feed lines exist. However, these systems and methods require additional hardware for the transmission and reception of data in a solar panel system.
Many of the issues involved in sending communication signals over DC power lines also exist when sending such signals over the AC power grid. The properties of the transmission medium vary greatly, and the amount and nature of noise sources are very difficult to predict.
However, there are some important differences too. On the AC power grid, the loads are mostly of an inductive nature, and some loads may be resistive and a few subtly capacitive. In contrast, on a DC power bus, virtually all loads and sources are capacitive in nature. Another key difference lies in the use of transformers to convert between different voltage levels on an AC grid that cannot be similarly employed on a DC bus. Hence, a majority of sources and loads on a DC bus employ electronic DC-DC converters, which are very strong noise emitters.
There are many challenges to communicating digital data quickly and reliably over a set of wires intended to conduct electrical energy. For a variety of reasons, the signal carrier frequency should not exceed 500 kHz, so as to avoid the antenna effects, and avoid excessive signal attenuation and unintentional electromagnetic radiation. Power line carrier frequency is typically between 90 kHz and 490 kHz for small power line network line for, for example, a residence. A larger commercial power line installation must further limit the maximum carrier frequency so that the effective length of the wires does not exceed ⅛ of the carrier wave length.
Low carrier frequency in turn means that the rate of signal than can be modulated on such a carrier is also very low, so that a certain payload to carrier ratio is maintained. The signal rate that can be carrier by a frequency is also limited by severe noise and attenuation typical to power lines. This is because the slower the signal rate, the more energy is carrier by a single symbol (bit), and with more energy in a bit, the less likely it is to be corrupted in transmission.
There are several types of products on the market at this time to address the needs of power line communications. Broadband communication products deliver local area network performance but can not handle more than just a handful of nodes on the network. Such products lack the robustness and reliability that is needed for a sensor network.
The narrowband power line communication products can be further divided into two types: the solutions involving a single or dual carrier tones and the newer solutions mostly involving a kind of spread spectrum technique involving a large number of carrier tones or a digitally synthesized equivalent.
Solar system installers take a large guard band (or safety margin) to make sure the voltages don't cross the 600V or 1000V limits in the United States and the European Union, respectively. That limitation inhibits them from installing more solar panel modules, often referred to as “modules” or “panels,” in series to reduce the cost of combiner boxes or string inverters. When solar modules are connected in series or in mesh configurations, there can be a problem in which weaker modules not only produce less energy but also affect other modules' capabilities to deliver energy in the same string or wiring section.
In the solar panel industry, the pressure to reduce costs is increasing. While certain features may be desired, there is more pressure to dramatically reduce cost, which means delivering added functionality at little or virtually no cost.